In wireless communication technologies, when a base station such as an Evolved Node B (eNodeB, eNB) sends data using multiple antennas, a spatial multiplexing scheme can be adopted to enhance the data transmission rate, namely, different data are transmitted at different antenna locations using the same time-frequency resource at a sending end, and likewise, a receiving end such as a User Equipment (UE) receives data by using multiple antennas. In the case of a single user, the resources of all antennas are allocated to the same user, this user occupies exclusively a physical resource allocated to an base station side in a transmission interval, this way of transmission is called Single User Multiple-Input Multiple-Out-put (SU-MIMO); In the case of multiple users, a spatial resource of different antennas is allocated to different users, one user shares the physical resource allocated by the base station side with at least one other user in the transmission interval, wherein the way of sharing may be a Space Division Multiple Access scheme or a Space Division Multiplexing scheme, and this way of transmission is called Multiple User Multiple-Input Multiple-Out-put (MU-MIMO). Wherein, the physical resource allocated by the base station side refers to the time-frequency resource, The eNB needs to provide the data in those two modes to the UE if a transmission system is to simultaneously support both SU-MIMO and MU-MIMO. Both in the SU-MIMO mode and the MU-MIMO mode, the UE needs to know the Rank used by the eNB for transmitting MIMO data to the UE, in the SU-MIMO mode, the resources of all antennas are allocated to the same user, the number of layers used for transmitting the MIMO data just equals to the Rank used by the eNB for transmitting the MIMO data; In the MU-MIMO mode, the number of layers used for transmission to one user is less than the total layer number used by the eNB for transmitting the MIMO data; If a handover between the SU-MIMO and the MU-MIMO modes is to be performed, the eNB needs to inform the UE of different control data in different transmission modes.
In a Long Term Evolution (LTE) system, the control signallings to be transmitted on uplink includes an Acknowledgement/Negative Acknowledgement (ACK/NACK) message and three forms reflecting downlink physical Channel State Information (CSI): CQI, Pre-coding Matrix Indicator (PMI), and Rank Indicator (RI).
The CQI is an indicator for judging whether the quality of a downlink channel is good or bad. In a 36-213 protocol, the CQI is represented by an integer value from 0 to 15, which represents different CQI levels respectively, wherein different CQI corresponds to respective Modulation and Coding Scheme (MCS) as shown in Table 1. The selection of the CQI level should conform to the following rule:
The selected CQI level should make the Block Error Rate of a PDSCH (Physical Downlink Shared Channel) transmission block corresponding to the CQI not exceed 0.1 in corresponding MCS.
Based on a non-restrictive detecting interval in a frequency domain and a time domain, the UE will obtain the highest CQI value corresponding to each maximum CQI value reported in an uplink subframe n; the range of a CQI index is from 1 to 15 and satisfies the following condition (the CQI index is 0 if the CQI index 1 does not satisfy this condition): when a single PDSCH transmission block is being received, the Error Rate does not exceed 0.1. The PDSCH transmission block contains a joint information: a modulation scheme and a transmission block size corresponding to one CQI index and an occupied set of downlink physical resource blocks, i.e., CQI reference resources. Wherein, the highest CQI value refers to the maximum CQI value when the block error rate (BLER) is guaranteed to be no greater than 0.1, which helps to control resource allocation. Generally speaking, the smaller the CQI value, the more the resources occupied, and the better the BLER performance.
The combination of the transmission block size and the modulation scheme corresponds to a CQI index, which specifically includes the following conditions:
1. According to a relevant transmission block size table, the combined information for performing PDSCH transmission on the CQI reference resource may be informed by using a signalling.
2. The CQI index may indicate the modulation scheme
3. The effective channel code rate generated by the combined information containing the transmission block size and the modulation scheme applied in the reference resources is the most accessible effective channel code rate that can be characterized by the CQI index. When there are more than one combined information exists and the combined information may all generate equally accessible effective channel code rates characterized by the CQI index, then the combined information with a minimum transmission block size is adopted.
Each CQI index corresponds to a modulation scheme and a transmission block size; the transmission block size has a definite corresponding relationship with the number of Physical resource blocks (NPRB), and the code rate may be calculated according to the transmission block size and the size of NPRB.
TABLE 14 bit CQI tableCQI indexmodulationcode rate × 1024efficiency0out of range1QPSK (Quadrature Phase780.1523Shift Keying)2QPSK1200.23443QPSK1930.37704QPSK3080.60165QPSK4490.87706QPSK6021.1758716QAM (Quadrature3781.4766Amplitude Modulation)816QAM4901.9141916QAM6162.40631064QAM4662.73051164QAM5673.32231264QAM6663.90231364QAM7724.52341464QAM8735.11521564QAM9485.5547
A CQI appeared in the LTE has various definitions, and the CQI may be classified according to different principles:
1. According to a measuring bandwidth, it is classified into wideband CQI and subband CQI:
The wideband CQI refers to a channel state indication for all subbands, which leads to a CQI information of set S of subbands;
The subband CQI refers to the CQI information for each subband. The LTE divides the Resource Blocks (RB) corresponding to an effective bandwidth into several RB groups according to different system bandwidths, each RB group is called a subband.
The subband CQI may be further classified into an all-subband CQI and a selecting M best subbands (Best M) CQI; The all-subband CQI reports the CQI information for all subbands; the best M CQI selects M subbands from the set S of subbands, reports the CQI information of these M subbands, and reports the location information of the M subbands simultaneously.
2. According to the number of code stream, it is classified into single stream CQI and double stream CQI:
The single stream CQI is applied to Closed-loop spatial multiplexing of RI=1, single antenna transmitting port 0, port 5, Transmit diversity, and MU-MIMO, in which case the UE reports the CQI information of a single code stream;
The double stream CQI is applied to a Closed-loop spatial multiplexing mode. To an Open-loop spatial multiplexing mode, as a channel state information is unknown, and equalization processing is performed on double stream characteristics in preceding. therefore the CQIs of 2 code streams are equal under Open-loop spatial multiplexing.
3. According to a CQI representing method, it is classified into absolute value CQI and Differential CQI:
The absolute value CQI is the CQI index represented with 4 bits in Table 1;
The Differential CQI is a CQI index represented with 2 bits or 3 bits; The Differential CQI is further classified into the Differential CQI of a second code stream relative to a first code stream, the Differential CQI of a subband CQI relative to a subband CQI.
4. According to a CQI reporting scheme, it is classified into wideband CQI, UE selected (subband CQI), and High layer configured (subband CQI)
The wideband CQI refers to the CQI information of the set S of subbands;
The UE selected (subband CQI) is the Best M CQI feeding back the CQI information of the selected M subbands and reporting locations of the M subbands simultaneously;
The High layer configured (subband CQI) is the all-subband CQI that feeds back one CQI information for each subband.
Both the High layer configured and the UE selected are feedback schemes of the subband CQI, under a non-periodic feedback mode, subband sizes defined by these two feedback schemes are not the same; Under the UE selected mode, the size of the M is further defined.
In a LTE system, ACK/NACK is transmitted with a format 1/1a/1b (PUCCH format1/1a/1b) on a Physical Uplink Control Channel (PUCCH), and on a Physical Uplink Shared Channel (PUSCH) if the UE needs to transmit uplink data; the feedback of CQI/PMI and RI may be a periodic feedback or may be a non-periodic feedback Specific feedbacks are as shown in Table 2:
TABLE 2Uplink physical channel corresponding to a periodicfeedback and a non-periodic feedbackperiodic CQInon-periodic CQIscheduling modereport channelreport channelfrequencyPUCCHnon-selectivityfrequency selectivityPUCCHPUSCH
Wherein, to the CQI/PMI and RI which are periodically fed back, if the UE does not need to transmit uplink data, then the CQI/PMI and RI which are periodically fed back are transmitted with the format 2/2a/2b (PUCCH format2/2a/2b) on the PUCCH: If the UE needs to transmit uplink data, then the CQI/PMI and RI are transmitted on the PUSCH; the CQI/PMI and RI which are non-periodically fed back are transmitted only on the PUSCH.
The following three kinds of downlink physical control channels are defined in an LTE Release 8 standard: Physical Control Format indicator Channel (PCFICH), Physical Hybrid Automatic Retransmission Request Indicator Channel (PHICH), and Physical Downlink Control Channel (PDCCH). Wherein, the PDCCH is configured to bear Downlink Control Information (DCI) including uplink and downlink scheduling information, and uplink power control information. A DCI format is classified into: DCI format 0, DCI format 1 DCI format 1A, DCI format 18, DCI format 1C, DCI format 1D, DCI format 2, DCI format 2A, DCI format 3, DCI format 3A and the like; Wherein a transmission mode 5 supporting the MU-MIMO utilizes the Downlink Control Information of DCI format 1D, and a Downlink power offset field □power-effect in DCI format 1D is configured to indicate the information for halving (i.e., −10 log 10 (2)) the power to a user in the MU-MIMO mode, as the MU-MIMO transmission mode 5 only supports the MU-MIMO transmission of two users; and through this Downlink power offset field, the MU-MIMO transmission mode 5 may support the dynamic handover between the SU-MIMO mode and the MU-MIMO mode. However, no matter in the SU-MIMO mode or the MU-MIMO mode, this DCI format only supports the transmission of one stream for one UE; although LTE Release 8 supports a single-user transmission of at most two streams in transmission mode 4, since the handover between transmission modes can only be done semi-statically, therefore the dynamic handover between a single-user multi-stream transmission and a multi-user transmission can not be achieved in LTE Release 8.
In LTE Release 9, in order to enhance downlink multi-antenna transmission, a double-stream Beamforming transmission mode, which is defined as transmission mode 9, is introduced, and a DCI format 2B is added to the Downlink Control Information to support the transmission mode. There is an identifier bit for scrambling identity (SCID) in the DCI format 2B which is to support two different scrambling sequences, an eNB may allocates the two scrambling sequences to different users so as to multiplex multiple users at the same resource. Moreover, when only one transmission block is Enabled, a new data indicator (ND) bit corresponding to a Disabled transmission block is also used for indicating an antenna port in the case of single layer transmission.
Moreover, in an LTE Release 10, in order to further enhance downlink multi-antenna transmission, a new Closed-loop spatial multiplexing transmission mode, which is defined as a transmission mode 10, is added, this transmission mode can support SU-MIMO and MU-MIMO as well as the dynamic handover thereof. Moreover, this transmission mode also supports 8-antenna transmission. This new transmission mode has determined to use a Demodulation Reference Signal (DMRS) as a pilot frequency for demodulation, and the UE needs to acquire the location of the pilot frequency before making channel and interference estimation on the pilot frequency.
In Release R10, the UE is semi-statically configured, through a high level signalling, to receive PDSCH data transmission in accordance with the indication of the PDCCH of an UE-Specific search space based on one of the following transmission modes:
Mode 1: Single-antenna port; port 0;
Mode 2: Transmit diversity;
Mode 3: Open-loop spatial multiplexing;
Mode 4: Closed-loop spatial multiplexing;
Mode 5: Multi-user MIMO;
Mode 6: Closed-loop Rank=1 precoding;
Mode 7: Single-antenna port; port 5;
Mode 8: double-stream transmission, i.e., double-stream beam shaping;
Mode 9: spatial multiplexing of at most 8 layers.
In Release R10, transmission mode 9 and a Channel-State Information-Reference Symbol (CSI-RS) are newly added. Transmission mode 9 performs channel measurement based on the CSI-RS, so as to calculate and obtain CQI. Other transmission modes perform channel measurement based on a cell-specific reference signal (CRS), so as to calculate CQI. In Release R10, some CSI-RS parameters are also added correspondingly for characterizing attribute. Compared with the CRS in R8, some parameters are similar. some parameters are newly added. For example, there is a similar CRS port number in R8, while a CSI-RS subframe configuration period parameter is newly added, The following parameters are cell-specific and are configured by a high level signalling for the definition of CSI-RS, including:
a CSI-RS port number, a CSI-RS configuration, a CSI-RS subframe configuration parameter (ICSI-RS), a subframe configuration period (TCSI-RS), a subframe deviator, and an assumed Pc of an UE applied to a CSI feedback with reference to a PDSCH transmitting power.
In R10, to the transmission mode 9, as the new concept of “double-codebook” or “double-PMI” is introduced, therefore two PMIs needed to be fed back; to 8 antennas, a first PMI indicates the channel state information of a wideband, a second PMI indicates the channel state information of a subband, and the complete precoding matrix information can only be obtained when both PMIs are obtained, wherein the subband includes the case of the wideband, i.e., the wideband is taken as one special case of the subband, for example the second PMI also may be of wideband; to 2 antennas and 4 antennas, the first PMI indicates a unit matrix, and the second PMI is equivalent to the PMI of the original R8 protocol.
To the new transmission mode 9 of the R10 protocol, lack of consideration to CSI-RS and PRS when determining and calculating CQI will cause transmission mode 9 cannot accurately use the CRS or CSI-RS to achieve channel measurement, and thereby cannot obtain accurate channel quality information in the case of transmission mode 9, which will seriously reduce the flexibility and performance indicator of the system.